Low bandgap mid-infrared thermophotovoltaic arrays based on InAs

Highlights

• We demonstrate low bandgap InAs-based thermophotovoltaic (TPV) arrays.

• These TPVs can operate with heat sources at temperatures as low as 345 °C.

• Low bandgap TPV arrays could be used to generate electricity from waste heat.

Abstract

We demonstrate the first low bandgap thermophotovoltaic (TPV) arrays capable of operating with heat sources at temperatures as low as 345 °C, which is the lowest ever reported. The individual array elements are based on narrow band gap InAs/InAs_0.61Sb_0.13P_0.26 photodiode structures. External power conversion efficiency was measured to be ∼3% from a single element at room temperature, using a black body at 950 °C. Both 25-element and 65-element arrays were fabricated and exhibited a TPV response at different source temperatures in the range 345–950 °C suitable for electricity generation from waste heat and other applications.

Introduction

There is continuing interest in thermophotovoltaic (TPV) devices because they can provide an attractive method for the direct conversion of heat into electricity in a wide variety of applications, and in particular for industrial waste heat recovery and silent or remote power generation. The optimum TPV cell bandgap depends on the emitter blackbody temperature, and following the thermodynamic detailed balance model [1], in the ideal case where radiative recombination is dominant, the maximum TPV cell efficiency is ∼35% for source temperatures between 1200 and 2500 K, such that the optimum bandgap falls in the range 0.2–0.5 eV [2]. To date previous work has concentrated on TPV devices matched to high temperature sources using semiconductors with larger bandgaps such as silicon (E_g = 1.1 eV), InGaAs [3] on InP (typically E_g = 0.5–0.73 eV, but which is limited by lattice mismatch to the higher bandgaps), or InGaAsSb on GaSb (constrained to E_g = 0.5 eV by a miscibility gap). There have been some studies of the development and characterisation of InAs based diodes for lower temperature TPV applications, but, these reports concern mainly epitaxial growth and characterisation of individual elements [4], [5]. Meanwhile, although there are currently active investigations into quantum cascade based or multiple-junction TPVs, there are still no TPV arrays capable of electricity generation using thermal source temperatures below 1000 °C [6], [7]. In this work we have developed an approach using InAs with a bandgap of 0.32 eV (300 K) and demonstrate prototype InAs-based TPV arrays. These devices have a lower bandgap than conventional GaSb or InGaAs cells and are well-matched to cooler thermal sources at temperatures ∼500 °C.